Method and apparatus of coating articles

ABSTRACT

A coating such as liquid milk chocolate is applied to articles such as confectionery bars. The bars are conveyed by conveyor under a curtain of liquid chocolate issuing through an outlet slot in a trough. A layer of air is caused to flow through the outlet slot in the trough so as to modify the flow characteristics of the curtain. The layer of air permits a curtain of even thickness to be achieved.

This application is a divisional of U.S. application Ser. No. 09/600,769filed Nov. 9, 2000, now U.S. Pat. No. 6,730,344 which is the U.S.National Phase application of International Application No.PCT/GB99/00158, filed Jan. 18, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, in a first of its aspects, to a method of and anapparatus for applying a coating to articles, eg an edible coating tofood articles. The invention is particularly, but not exclusively,concerned with the application of edible coating materials which exhibitnon-Newtonian behaviour, for example chocolate, to articles ofconfectionery and the like. The present invention also relates, in asecond of its aspects, to an improved method of forming a curtain ofmaterial eg edible material which can be used to coat articles egarticles of food or which can be used in other ways in the formation ofarticles, eg articles of food.

2. Description of Related Art

It is well known to enrobe articles, of food such as chocolateassortments, confectionery bars, biscuits, cookies and cakes with alayer of chocolate. This coating process is known as chocolate enrobingand is traditionally effected by moving the articles on a mesh-typeconveyor belt through a curtain of liquid chocolate whose consistency iscarefully controlled. However, it is difficult to achieve the desiredcoating because of the high viscosity. It is therefore common practiceto subject the articles to a greater than needed coating, thencontrolling the amount of chocolate remaining on the articles by blowingby air from fans and using vibration to remove the excess.

Also, the temperature of chocolate cannot be increased so as to reduceits viscosity as it will lose its temper, causing problems of incorrectfat crystallisation which can deleteriously affect the appearance and/oreating quality of the chocolate. Thus, it is common for enrobingchocolate to have a higher fat content than standard chocolate used formaking chocolate bars in order to reduce its viscosity. This has adversecost implications.

In order to establish the curtain of chocolate, it is known to allowchocolate to pass under the action of gravity through an outlet slot inthe bottom of a trough having inclined side walls leading to the slot.This type of apparatus has a relatively low throughput because of thehigh viscosity of the chocolate and the relatively low rate at which itcan flow through the outlet slot. The common solution to this problem isto use a wider slot, which results in a thicker curtain which thenrequires removal of more excess from the articles. Because of thephysical characteristics of the chocolate which passes through, theslot, the curtain can “neck” to a substantial extent. In other words,the width of the chocolate curtain becomes substantially less than thelength of the slot from which it issues. This means that the effectivecover of the curtain over the width of the conveyor belt used to carrythe articles through the curtain is reduced.

Another known form of apparatus for producing a chocolate curtainutilises a roller along which liquid chocolate is distributed andcarried to a blade which causes the layer of chocolate on the roller tobecome detached and thereby establish the curtain. This can providehigher coating rates with a better control of curtain thickness, butdifficulties still arise in coating.

With both of the above types of known apparatus, the amount of chocolatein the descending curtain is greatly in excess of that required to coatthe articles. The excess drains through the mesh-type conveyor belt andneeds to be recycled and its condition carefully controlled.

SUMMARY OF THE INVENTION

It is an object of a first aspect of the present invention to obviate ormitigate at least some of the above disadvantages.

In accordance with said first aspect of the present invention, there isprovided a method of applying a coating to articles, comprising thesteps of:

-   (i) providing a curtain of solidifiable liquid coating material;-   (ii) effecting relevant movement between articles to be coated and    the curtain so as to coat the articles with the solidifiable liquid    coating material; and-   (iii) subjecting the solidifiable liquid coating material to the    action of at least one stream of gas under pressure whereby to    modify the flow characteristics of the curtain.

Also in accordance with said first aspect of the present invention,there is provided apparatus for applying a coating to articles,comprising:

-   (i) supply means arranged to provide a curtain of solidifiable    liquid coating material;-   (ii) means for effecting relative movement between articles to be    coated and the supply means whereby in use the articles are coated    with the solidifiable liquid coating material in the curtain; and-   (iii) means arranged to subject the solidifiable liquid coating    material to the action of at least one stream of gas under pressure    whereby to modify the flow characteristics of the curtain.

Preferably, the articles are articles of food and the coating materialis an edible coating material.

In the case where the present invention is used in a coating apparatusof the type in which the coating material is caused to flow along asurface of the supply means (eg a trough) towards an outlet slot throughwhich the coating material flows under the action of gravity to form thecurtain, it is preferred for said at least one stream of gas to beintroduced between the coating material and the surface of the supplymeans. In this way layer of gas can be introduced between the surfaceand the coating material as it flows towards the outlet slot.Preferably, in the case of a trough where the coating material flowsover opposed surfaces towards the outlet slot, a layer of gas isintroduced between the coating material and each of the opposedsurfaces. This can not only substantially reduce the resistance to flowof the coating material over the surfaces, but can also reduce theviscosity of the coating material if it is of a type whose viscosity isreduced when subjected to shear.

It is particularly preferred to cause said at least one stream of gasunder pressure to become attached to the surface of the supply means soas to assist in establishing the layer of the gas between the surfaceand the coating material. This may be achieved by positioning one ormore gas-admission slots in such a way as to direct the gas against thesurface of the supply means. The spacing between the outlet slot and theor each gas-admission slot depends upon the nature of the coatingmaterial and the geometry of the supply means, which may comprise atrough having V-shaped walls defining opposed surfaces which convergetowards the outlet slot. If the or each gas-admission slot is disposedtoo close to the outlet slot, then the flow of gas through the outletslot may actually restrict the flow of coating material therethrough. Onthe other hand, if the or each gas admission slot is disposed too faraway from the outlet slot, the coating material flowing over the surfacemay become re-attached to the surface of the supply means before itreaches the outlet slot.

In the case where the above-mentioned trough is employed, it is withinthe scope of the present invention to provide said at least one streamof gas under pressure at one or both convergent opposed surfaces of thetrough leading to the outlet slot.

Said at least one stream of gas under pressure may be applied to thecoating material after the curtain has been established in order tochange the direction of the curtain and/or a physical property of thecoating material forming the curtain. It is also within the scope of thepresent invention to subject the coating material to the action of atleast one stream of gas both before and after the curtain has beenestablished.

A curved surface may be provided adjacent to part of the curtain, andmeans may be provided for causing a stream of gas to flow over thecurved surface by virtue of the Coanda effect and to use this to inducea change in the direction of travel of the curtain. In this way, it ispossible to control the direction of flow of the curtain from any anglefrom vertical to substantially horizontal. This effect can be usedwhether or not the coating material is subjected to the action of atleast one stream of gas under pressure before the curtain isestablished. In this regard, the curtain may be established by flow ofthe coating material through an outlet slot or by distributing thecoating material over the length of a roller and causing it to betransported to a blade which removes the coating material from theroller and thereby establishes the curtain.

It is within the scope of the present invention to use one or morecurtains of coating material to coat the articles and to control thedirection of movement of these curtains simultaneously or independentlyin such a way as to ensure maximum coverage. For example, one of thecurtains may be controlled so that its direction of movement is an acuteangle (e.g. 45°) relative to the direction of relative movement betweenthe articles and the curtain, whilst the other curtain can be controlledso that its direction of movement is at an obtuse angle (e.g. 135°) withrespect to said direction of relative movement. In this way, coating ofupstream and downstream ends of the articles may be facilitated.

In certain embodiments, the control of the pressure of the stream of gascan be employed to control the speed of descent of the curtain. Thus, bycontrolling the rate of descent of the curtain and the rate of relativemovement between the articles and the curtain, a variety of differenteffects can be achieved. For example, if the rate of descent of thecurtain is matched with the rate of relative movement, then a smoothcoating can be achieved. If the rate of curtain descent is greater thanthe rate of relative movement, then a surface patterning effect can begachieved by the resultant folding of the applied-curtain onto thearticles. On the other hand, if the rate of descent is less than therate of relative movement, a degree of stretching of the coatingmaterial as it becomes attached to the articles may be achievable withresultant thinning of the layer of coating material applied to thearticles. The effects achieved will also depend upon the physicalproperties of the coating material.

The present invention is applicable to the use of non-Newtonian liquidssuch as chocolate or Newtonian liquids such as caramel as coatingmaterials.

In the case of chocolate (or other non-Newtonian liquid, a liquid whoseviscosity reduces when subjected to shear), a very high degree ofcontrol is achievable because the stream of gas under pressure can becaused to contact the surface of the chocolate in such a way as toreduce its viscosity by application of a shear force. This has theparticular advantage that the chocolate flows much more easily but thenrapidly thickens once the shear force has been removed. The applicationof the stream of gas under pressure to the chocolate before the curtainhas been established can enable the previously mentioned necking problemto be mitigated and can also enable a much higher throughput to beachieved for a given size of coating apparatus. Because of the viscosityreduction achieved, it is possible to coat with a much higher viscositychocolate than has heretofore been considered possible. For example, it,is possible to coat with relatively viscous tempered chocolate, ratherthan having to coat with a chocolate composition having an increased fatcontent and subsequently lowered tempered viscosity in order toestablish and maintain the desired liquid curtain. The need to effectair blowing and/or vibration on the coated articles may be obviated ormitigated. The present invention permits a curtain of even thickness tobe achieved and may also enable a thinner curtain to be produced thanhas heretofore been possible.

Conveniently, the gas is air. The temperature of the gas may besubstantially the same as that of the solidifiable liquid coatingmaterial. This is particularly advantageous in the case where thematerial is liquid chocolate.

It will be appreciated that the present invention in its first aspectinvolves the control of a curtain of solidifiable liquid coatingmaterial for the purpose of coating or enrobing articles. However, itwill be appreciated that similar techniques can be employed forcontrolling a curtain of a solidifiable liquid material for use in theproduction of other articles. For instance, the curtain can becontrolled for the purpose of enabling a layer of the material to bedeposited into a mould or moulds (e.g. to produce shells of solidifiedmaterial which can then be used to contain filling material), or onto aconveyor for solidification as a layer thereon which can be subsequentlycut to size or otherwise shaped. The fact that the curtain can be veryaccurately controlled in terms of the thickness of the curtain and/orits angle/speed of descent means that a close control over the thicknessand/or texture of the deposit can be obtained which can be difficult toachieve with standard confectionery shell technology.

Thus, in its second aspect, the present invention resides in a method ofcontrolling a curtain of a solidifiable liquid composition comprisingthe steps of:

-   (i) providing a curtain of solidifiable liquid material; and-   (ii) before, during and for after step (i), subjecting the    solidifiable liquid material to the action of at least one stream of    gas under pressure whereby to modify the characteristics of the    curtain.

Also in accordance with said second aspect of the present invention,there is provided apparatus for controlling curtain of a solidifiableliquid composition comprising:

-   (i) supply means arranged to provide a curtain of solidifiable    liquid coating material; and-   (ii) means arranged to subject the solidifiable liquid coating    material to the action of at least one stream of gas under pressure    whereby to modify the characteristics of the curtain.

The method and apparatus may further include provision for (a)depositing the modified curtain of solidifiable liquid composition toform a layer in a mould or on a surface, and (b) solidifying thedeposited composition.

The solidifiable liquid composition is preferably an edible composition.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of one embodiment of an apparatus accordingto the present invention, where, for ease of demonstration, only onelongitudinal trough surface is shown with an air supply,

FIG. 2 is a side view of a trough forming part of the apparatus of FIG.1, and

FIG. 3 is a schematic view of a second embodiment of apparatus accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2 of the drawings, the apparatusillustrated therein is for enrobing confectionery bars with a layer ofchocolate. The apparatus comprises a mesh-type conveyer belt 10 carryingconfectionery bars 12 to be coated horizontally from right to left asviewed in FIG. 1. A liquid chocolate supply trough 14 is spaced abovethe conveyor 10 and comprises V-shaped walls 14 a and 14 b leading to adownwardly opening outlet slot 14 c. The trough 14 contains liquidchocolate 16 which is to be used for coating the confectionery bars 12to form coated confectionery bars 18.

The trough 14 contains an additional wall 14 d which is inclined at anacute angle relative to the wall 14 b and which terminates about 10 mmabove the outlet slot 14 c which, in this embodiment, has a width ofabout 2 mm. The walls 14 b and 14 d together define a downwardlyconvergent plenum chamber 20 terminating in an air-admission slot 22.The slot 22 has a width of 0.2 mm and extends for the whole length ofthe outlet slot 14 c, and is disposed about 10 mm above the outlet slot14 c of the trough 14. The plenum chamber 20 is connected with a sourceof pressurized air, the pressure of which is controlled by a controller26. Although not shown in the drawings, the wall 14 a is likewiseprovided with an additional wall defining an identical air-admissionslot like slot 22.

Disposed below the conveyor 10 is a tank 24 which also contains liquidchocolate 16. A pump (not shown) serves to pump the liquid chocolate 16from the tank 24 to the trough 14 via pipework 28.

In use, the conveyor belt 10 is operated to move the confectionery bars12 in a path which carries them under the outlet slot 14 c of the trough14. The chocolate 16 in the trough 14 is typically maintained at atemperature in the range of 28 to 31° C. and travels through the slot 14c under the action of gravity so as to produce a curtain 30 of liquidchocolate through which the confectionery bars 12 pass. The curtain 30extends perpendicularly across the conveyor belt 10 which carries aplurality of rows of the confectionery bars 12, although only one row ofbars 12 is illustrated in the drawings. The resultant coated bars 18 arecarried by the conveyor 10 and excess chocolate drips through the holesin the screen conveyor 10 and back into the tank 24 for recirculation.

During this time, air under pressure is supplied to the plenum chamber20 so that it is ejected through the air-admission slot 22 so as tobecome attached to that portion of the wall 14 b which lies between theslots 22 and 14 c. The result of this is that a layer of air is insertedbetween the chocolate 16 passing towards the outlet slot 14 c and thewall 14 b immediately upstream of the slot 14 c. The same occurs at thewall 14 a. This substantially reduces the friction between the chocolateand the walls. Additionally, the pressurised air exerts a shear force onthe adjacent surface of the chocolate, thus reducing the viscosity ofthe chocolate in the region of the outlet slot 14 c. This improves theflowability of the chocolate so that it substantially increases the flowrate through the slot and also mitigates the necking problem whereby thewidth of the curtain 30, i.e. the dimension perpendicular to the planeof the drawing, can be maintained substantially the same as the lengthof the slot 14 c.

In one experiment, it was found that no less than a 70% increase in theflow rate through the slot 14 c could be achieved using an air supplypressure of 2 psig, as compared to the situation where no air issupplied through the gas admission slot 22. Although, substantiallyimproved results could be achieved with air pressures as low as 0.5 psigand up to about 3 psig. It will be understood that the shear effect isproduced because the air is moving at a greater rate than the chocolatewith which it is in contact.

The above-described method enables improved control to be achieved,which can lead to the following advantages:

-   (a) lighter chocolate coatings,-   (b) more precise coating with less excess deposit,-   (c) less variation in deposit across the conveyor belt,-   (d) faster enrobing speeds,-   (e) lower proportion of chocolate to be recycled,-   (f) less build-up of chocolate on the edges of the bars, leading to    better edge definition,-   g) selective production of textured or plain coatings by adjustment    of air pressure and conveyor belt speed.-   (h) avoidance of the need to use enrobing chocolate (which has a    high fat content to decrease its viscosity when liquid), thereby    enabling the use of regular or even lower fat chocolate.

Referring now to FIG. 3 of the drawings, there is illustrated anapparatus also in accordance with the present invention for altering thedirection of descent of chocolate curtain 30. The chocolate curtain 30may be one which has been produced as described hereinabove withreference to FIGS. 1 and 2. Alternatively, it may be a conventionallyproduced chocolate curtain which has been formed without introduction ofan air-stream into trough 14. As a further alternative, it may be aconventionally produced curtain formed by distributing a layer of liquidchocolate onto the surface of a roller and then detaching the layer fromthe roller by means of a blade.

In, the apparatus of FIG. 3, there is provided a cylindrical plenumchamber 40 which is horizontally disposed to one side of the curtain 30above the conveyer 10 and which extends for greater than the full widthof the curtain 30. The plenum chamber 40 may conveniently be mounted onthe trough 14 so that it can be positioned close to the outlet 14 c. Theplenum chamber 40 has a pressurised air inlet 42 and a row of upwardlydirected air outlets 44 extending over the length of the plenum chamber40. An angled cap 46 is secured to the outer periphery of the plenumchamber 40 along a longitudinal side edge thereof which is remote fromthe curtain 30. The opposite longitudinal side edge of the strip 46 isspaced from the peripheral surface of the plenum chamber 40 so as todefine an air-exit slot 48. The slot 48 has a width of typically about0.2 mm. The plenum chamber 40 can be moved laterally horizontallyrelative to the curtain 30 so as to enable the gap between it and thecurtain 30 to be adjusted. Likewise, the plenum chamber 40 can be turnedabout its longitudinal axis to enable the position of the slot 48relative to the curtain 30 to be adjusted.

In use, air is supplied through the inlet 42 into the plenum chamber 40from whence it issues through the outlets 44 and thence through theoutlet slot 48. It is thus caused to adhere to the curved peripheralsurface of the plenum chamber 40 by virtue of the Coanda effect wherebyit follows the external periphery of the plenum chamber 40 for aconsiderable distance. The effect of this curved flow of air is to drawthe curtain 30 towards the plenum chamber 40, thus altering the angle ofdescent of the curtain 30. The angle of descent can be varied by varyingthe pressure of the air and/or by varying the positioning of the slot 48relative to the curtain 30. The pressure of the air can be varied bycontroller 26.

In FIG. 3, the plenum chamber 40 is shown on the downstream side of thecurtain 30 relative to the conveying direction of the confectionery bars12 through the curtain 30. Thus, the effect is to incline the directionof descent of the curtain 30 at an acute angle relative to the directionof movement of the confectionery bars 12. This can enable improvedeffects to be achieved. It is possible to lay the curtain 30 ofchocolate gently onto the surfaces of the bars 12 by appropriatelymatching the rate of descent of the curtain 30 to the speed and movementof the bars 12. It is also considered that, because of the angling ofthe curtain 30, it will be possible to improve coating of the leadingends of the confectionery bars 12.

However, it will be appreciated that it is possible to locate the plenumchamber 40 on the opposite side of the curtain 30, ie on the upstreamside thereof so as to cause the direction of descent of the curtain 30to extend at an obtuse angle relative to the conveying direction of theconfectionery bars 12. In this way, it is considered that an improvedcoating of the trailing ends of the confectionery bars 12 may beachievable. Also, further control over the effects produced can beachieved by altering the conveyor rate relative to the rate of descentof the curtain 30.

If desired, the confectionery bars 12 may be taken through more than onecurtain 30 with the curtains being disposed of the same or differentangles depending upon the effects required.

If desired, the confectionery bars may be passed through the curtaintwice, the first time for the purpose of effecting a main coatingoperation and a second time for the purpose of ensuring that the coatedbar is of the specified weight.

The curtain of chocolate (or another solidifiable liquid material)produced as described with reference to either or both of theillustrated embodiments may, instead of being used to enrobe articlessuch as confectionery bars, be used to form a layer of controlledproperties (eg thickness) into moulds as an alternative to conventionaldepositing technology, followed by cooling to solidify the layer. Such atechnique can be used to form shells for subsequent filling with afilling material. Alternatively, the curtain may be laid onto a conveyorto form a controlled Layer thereon which is subsequently solidified andcut to size to the desired shape.

1. An apparatus for coating articles, comprising: means for supplying a solidifiable liquid coating material, said supply means having a surface along which the solidifiable liquid coating material flows; an outlet slot positioned downstream of the supply means through which the solidifiable liquid coating material flows under the action of gravity to form a curtain; means for effecting relative movement between the articles and the supply means whereby in use the articles are coated with the solidifiable liquid coating material in the curtain; and means for introducing a first gas stream between the surface and the solidifiable liquid coating material so that flow characteristics of the curtain are modified, wherein the articles are articles of food and the solidifiable liquid coating material is an edible coating material.
 2. The apparatus of claim 1, wherein the edible coating material is chocolate.
 3. The apparatus of claim 1, wherein the supply means includes a trough having opposed surfaces leading towards the slot, and the first gas stream introducing means is arranged to introduce the first gas stream between the solidifiable liquid coating material and each of the opposed surfaces.
 4. The apparatus of claim 1, further comprising a controller for controlling a pressure of the first gas stream.
 5. An apparatus for coating articles, comprising: means for supplying a solidifiable liquid coating material, said supply means having a surface along which the solidifiable liquid coating material flows; an outlet slot positioned downstream of the supply means through which the solidifiable liquid coating material flows under the action of gravity to form a curtain; means for effecting relative movement between the articles and the supply means whereby in use the articles are coated with the solidifiable liquid coating material in the curtain; means for introducing a first gas stream between the surface and the solidifiable liquid coating material so that flow characteristics of the curtain are modified; and means for introducing a second gas stream to the solidifiable liquid coating material after the curtain has been established in order to change a direction of the curtain and/or a physical property of the solidifiable liquid coating material forming the curtain.
 6. The apparatus of claim 5, further comprising a curved surface positioned adjacent a portion of the curtain, wherein the second gas stream introducing means is arranged to cause the second gas stream to flow over the curved surface by virtue of a Coanda effect to induce a change in a direction of travel of the curtain.
 7. The apparatus of claim 5, further comprising a controller for controlling a pressure of the first and/or second gas streams. 